1. Field of the Invention
This invention relates generally to an automatic exposure and flash fire control system for a photographic camera apparatus, and more particularly, to a system for automatically controlling the firing of a flash of artificial illumination under conditions of varying ambient scene light intensity and camera-to-subject distance range.
2. Description of the Prior Art
In the photographic art, exposure control systems embodying scanning shutter blade elements which operate to vary exposure aperture areas with time during the exposure interval are well-known as indicated by U.S. Pat. No. 3,942,183, entitled "Camera with Pivoting Blades", by G. Whiteside, issued Mar. 2, 1976, in common assignment herewith. Such scanning shutter blade mechanisms generally include a pair of counter reciprocating shutter blade elements each having a primary aperture that traverses the optical axis of the camera during the exposure interval. The primary apertures are shaped so that upon overlying one another during counter movement of the blades, there is defined an effective exposure aperture value which increases to a maximum value in a determinate period of time.
Exposure control is provided by a pair of secondary photocell apertures in respective shutter blade elements which admit scene light to a photoresponsive element in correspondence with the scene light admitted to the focal plane during shutter blade movement through an exposure cycle. The output from the photoresponsive element is directed to an integrator circuit which triggers upon reaching an integration level corresponding to a desired exposure value to terminate the exposure interval by returning the shutter blade elements back to their initial scene light blocking position.
Shutter mechanisms of the aforementioned type are often arranged to operate in synchronism with a source of artificial illumination such as an electronic flash or strobe. The shutter blade mechanism and strobe are generally arranged to operate in either a high ambient scene light intensity mode of operation where no artificial illumination is provided or a low ambient scene light intensity mode of operation where the strobe is fired to provide a source of artificial illumination. Under conditions of low ambient scene light intensity where the strobe is expected to be fired, the scanning shutter blade mechanism may be stopped at an aperture value corresponding to the camera-to-subject distance as determined by focusing the objective lens. Systems of the aforementioned type are generally referred to as "follow focus" systems and the maximum aperture to which the scanning shutter blade elements are allowed to open is controlled by the rangefinding or focusing system of the camera in a manner as is more fully disclosed in U.S. Pat. No. 3,977,014, entitled "Follow Focus Exposure Control System with Improved Uniform Trim Control", by P. Norris, issued Aug. 24, 1976, in common assignment herewith.
Such a system need not acutally stop the opening shutter blade movement at a maximum effective exposure aperture as determined by the rangefinding or focusing system of the camera, but may instead, vary the time at which the strobe light is fired during the opening shutter blade movement as determined in correspondence with the rangefinding or focusing system of the camera. Since the duration of the storbe light is short in comparison to the time required for the shutter blade mechanism to scan from its scene light blocking position to its maximum exposure aperture defining position, the aperture defined by the shutter blade elements at the instant of strobe firing for practical purposes constitutes the effective aperture by which the exposure occurs. Such a system is more fully described in U.S. Pat. No. 3,478,660, entitled "Photographic Apparatus with Flash Exposure Control System", by E. Land, issued Nov. 18, 1969, in common assignment herewith. Range responsive flash firing systems of the aforementioned type can also be utilized in conjunction with sonar rangefinding devices as more fully described in U.S. Pat. No. 4,188,103, entitled "Range Synchronized Flash Photographic Apparatus and Method for Achieving Optimum Exposure", filed Apr. 21, 1978, in common assignment herewith.
Exposure and artificial illumination control systems of the aforementioned type are generally intended to provide a source of artificial illumination only during the low ambient scene light intensity mode of operation. However, there may also be conditions during high ambient scene light intensity modes of operation wherein it becomes desirable to provide artificial illumination to fill in the photographic subject against a brightly back lit scene as is more fully disclosed in U.S. Pat. No. 4,023,187, entitled "Exposure Control System with Fill Flash Race Condition", by E. Shenk, issued May 10, 1977, in common assignment herewith. The aforementioned artificial illumination control system operates under conditions of low ambient scene light intensity to fire the strobe light at a predetermined time period subsequent to the initiation of the exposure interval and under conditions of high ambient scene light intensity to fire the strobe light as a consequence of the time integration of the scene light intensity incident to the photoresponsive element reaching a predetermined value. This fill flash system, however, fails to provide a select ratio between that portion of the exposure which is directly attributable to the artificial scene illumination and the remaining portion of the exposure which is directly attributable to ambient scene light illumination over a determinate range of camera-to-subject distances.
Most recently, a photographic exposure and flash fire control system as disclosed in U.S. Pat. No. 4,192,587, entitled "Proportional Fill Flash", by A. LaRocque, et al., filed November 13, 1978, in common assignment herewith provided for the firing of a strobe in a fill flash mode of operation in a manner whereby a select ratio may be maintained between that proportion of the exposure which is directly attributable to the artificial scene illumination and the remaining proportion of the exposure which is directly attributable to the ambient scene light illumination. Such a select proportional fill flash is accomplished by providing a means whereby the light integration control circuit discounts the artificial illumination provided by the strobe. Toward this end, the system includes a sample and hold circuit which operates to sample the output voltage from a photoresponsive element and to transfer the sampled output voltage directly to a light integrating circuit. However, upon the firing of the strobe, the sample and hold circuit operates to hold the sampled voltage immediately prior to the firing of the strobe and to apply this sampled voltage to the light integrating circuit for the duration of the strobe pulse. The aforementioned sample and hold circuit, however, provides additional electronic complexity to the photographic exposure and flash fire control system.
Therefore, it is the primary object of this invention to provide an exposure and flash fire control system for providing a proportional fill flash in a simplified manner under varying conditions of ambient scene light intensity and camera-to-subject range.
It is a further object of this invention to provide an exposure and flash fire control system which operates in a simplified manner without the benefit of a sample and hold circuit to discount the artificial illumination provided by the source of artificial illumination so that a select proportion of the optimum film exposure value may be directly attributable to ambient scene light while the remaining proportion of the optimum film exposure value may be directly attributable to the artificial scene light provided by the source of artificial illumination.
Other objects of the invention will be in part obvious and will in part appear hereinafter. The invention accordingly comprises a mechanism and system possessing a construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure.